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Kinetic and Potential Energy

Investigation 3 – Concept Day








Kinetic and Potential Energy: Investigation 3

Concept Day


  • All energy on Earth ultimately comes from the Sun.
    • Much of the Sun’s energy is converted into stored chemical potential energy by the plant pigment chlorophyll in the process of photosynthesis.
    • The chemical energy stored in plants is used for their own growth and reproduction, but the consumption of plant material animals passes the Sun’s energy on down the food chain.
    • This chemical potential energy can be stored for enormous periods of time. When coal or oil is burned today, a reaction releases the potential chemical energy that was stored in it by living plants on sunny afternoons 300 to 400 million years ago!
  • One of the most common ways to convert stored chemical energy into kinetic energy is through a reaction known as combustion.
    • A combustion reaction is an exothermic reaction; that is, it gives off heat.
    • In a combustion reaction, a compound combines with oxygen-producing oxygen-containing products.

Note: In the following combustion reaction example, the simple hydrocarbon gas methane can react with oxygen:


Note: A more general form for a combustion reaction is:


Note: A hydrocarbon is a molecule that contains hydrogen and carbon. Fossil fuels, such as coal, oil, and methane are predominantly composed of hydrocarbons.



  • This slide is simply to accentuate the extreme power associated with combustion reactions and the release of kinetic energy from stored chemical potential energy.
  • The combustion reaction responsible for destructive forest fires like this is the same as for a useful and relaxing campfire.
  • Once a forest fire gets out of control it is difficult to stop. Why?
    • Look at the hydrocarbon combustion reaction above.
    • In a forest, there is essentially a limitless supply of reactants (hydrocarbon and oxygen) in very high concentrations.
    • Once started, the combustion can spread very quickly, traveling at speeds of over 10 km/hr and consuming tons and tons of material per hour.



  • This slide shows some of the many ways in which potential chemical energy is converted to kinetic mechanical energy.
  • Clockwise from top left, an old steam locomotive used wooden logs (loaded in the second car) to boil water and drive the steam engine. In a similar manner, the coal-burning navel vessel, the USS George Washington, was powered by steam. The “firemen” stoked the boilers to maintain steam pressure to drive the engine. To the lower right, international tennis star Novak Djokovic consumes a banana for energy and potassium during a match. Bottom center, gasoline is added to fuel an internal combustion engine. Bottom left, a horse feeds on hay to obtain chemical potential energy to pull a cart.



  • One of the most significant landmarks in engine design came with the invention of the 4-stroke internal combustion engine in 1876 by the German, Nicolaus Otto.
    • The design of the internal combustion engine was modified and perfected during the twentieth century and is still the major power source for self-propelled motor vehicles throughout the world today.

Note: The engine pictured here is a Ferrari 3.0 liter V12 F1 engine (1995) that produced 700 horsepower (522 kW) at 17,000 rpm. Four-stroke internal combustion engines work by using cylinder and piston technology. The details of the individual four “strokes” are explored in the next slide.



  • This slide shows the cycle of a 4-stroke internal combustion engine. 
    • A cylinder is drilled into a metal block that is precisely and tightly fitted with a piston that can move up and down within it.
    • The seal between the cylinder wall and the piston is air-tight.
  • The four strokes are as follows:
    • Stroke 1 – Intake: During this stroke, the piston is drawn downward. An intake valve is open during this stroke in which a mixture of fuel and air is drawn into the cylinder.
    • Stroke 2 – Compression: During this stroke, the piston is pushed upward, thereby compressing the fuel/air mixture into a very small volume at the top of the cylinder.
    • Stroke 3 – Power Stroke: A spark from a spark plug ignites the compressed fuel/air mixture. This initiates the combustion reaction:


The expanding carbon dioxide gas exerts a force on the piston and drives it down to the bottom of the cylinder.

    • Stroke 4 – Exhaust: The fourth and final stroke in the cycle is the exhaust stroke. During this stroke, the piston is pushed back up in the cylinder while an exhaust valve at the top of the cylinder is open. This expels the waste products of the power stroke (carbon dioxide, water vapor, and other gases), clearing the cylinder in preparation to repeat the cycle. At the end of this stroke, the exhaust valve closes, the intake valve opens and Stroke 1 begins again.
  • Four-stroke internal combustion engines typically contain four or more cylinders whose pistons are connected to a crankshaft.
    • Therefore, the power stroke from one cylinder drives the intake, compression, and exhaust strokes of the others in turn (see below).
    • The spinning of the crankshaft is ultimately harnessed to turn the wheels and tires.
    • It is a magnificent design that has had a useful lifespan of well over a century thus far.
  • Each power stroke represents the conversion of the chemical potential energy into kinetic mechanical energy. The chemical potential energy is stored in the chemical bonds of hydrocarbon molecules (gasoline) that were made hundreds of millions of years ago.




  • This slide shows the chemical reaction that will be performed in the Lab for Investigation 3.
  • It is not a combustion reaction. Nonetheless, one of the reaction products is a gas, carbon dioxide (CO2).

Note: The CO2 will be observed by students as bubbles in the reaction.

  • As the CO2 forms, the gas increases the volume of the reaction. In a closed system, this leads to pressure and mechanical energy.

Note: You will be able to directly explore the conversion of chemical potential energy into kinetic energy in Lab.



  • No goggles or gloves are necessarily required for the experiment for Investigation 3.
  • This is because, while acetic acid is the reactive component of vinegar, it is present at a very low concentration.